We report the analysis of an extensive set of spectroscopic data of the O(f
) supergiant HD 192639. A Fourier analysis of our time-series reveals a rec
urrent variability with a "period" of roughly 4.8 days which is most promin
ent in the absorption components of the He II X 4686 and H alpha P-Cygni pr
ofiles. The same periodicity is also detected in the blue wing of several a
bsorption lines (e.g. H beta). The variations of the absorption components
correspond most probably to a cyclical modulation of the amount of stellar
wind material along the line of sight towards the star. The 4.8-day period
affects also the morphology of the double-peaked He II lambda 4686 and HQ.
emission components, although these emission components display also variat
ions on other (mainly longer) time scales. The most likely explanation for
the 4.8-day modulation is that this cycle reflects: the stellar rotational
period (or half this period). We find that the most important observational
properties can be explained - at least qualitatively - by a corotating int
eraction region or a tilted confined corotating wind.